1. Field of the Invention
The present invention relates generally to fuel injection control apparatus and method for a variably operated engine valve equipped internal combustion engine and, more specifically, relates to a technique of preventing a variation in a pulsewidth Tp of a fuel injection quantity signal outputted to a fuel injector of an engine cylinder.
2. Description of the Related Art
In order to execute accurately a fuel injection quantity control or an air-fuel ratio control in an engine having a variably operated engine valve in which open/closure timings of an intake valve(s) is variably controlled, it is necessary to calculate a cylinder intake-air quantity, with a cylinder volume which is substantially varied according to a control over the closure timing of the intake valve(s) taken into consideration.
A European Patent Application Publication No. EP 1 074 716 A2 published on Feb. 7, 2001 (which corresponds to a U.S. patent application Ser. No. 09/634,008 which has been allowed on Jul. 27, 2001 and corresponds to a Japanese Patent Application First Publication No. 2001-50091 published on Feb. 23, 2001) exemplifies a previously proposed internal cylinder intake-air quantity calculating apparatus. In details, in this previously proposed internal cylinder intake-air quantity calculating apparatus, an actual closure timing of the intake valve is detected, an internal cylinder volume air quantity is calculated on the basis of the cylinder volume calculated from the actual closure timing of the intake valve and a fresh-air rate within the cylinder. Then, a mass air quantity within an intake manifold is calculated. Then, a cylinder intake-air quantity (mass air quantity) is calculated on the basis of the internal cylinder volume air quantity, the mass air quantity within the intake manifold, and an intake air manifold volume. In this way, the cylinder intake-air quantity is accurately calculated according to the above-described calculation procedure and the fuel injection quantity (fuel injection pulsewidth Tp) is calculated on the basis of the cylinder intake-air quantity.
However, since, in the above-described previously proposed internal cylinder intake-air quantity calculating apparatus, the cylinder intake-air quantity is calculated according to a detected value of the intake valve closure timing even in a case where the closure timing of the intake valve is in a steady state, the actual intake valve closure timing detected value (VTCNOW) is varied due to a load variation or bit-error so that the fuel injection pulsewidth Tp is accordingly varied. Consequently, a variation in the air-fuel ratio occurs and a driveability of the engine becomes reduced.
It is, hence, an object of the present invention to provide fuel injection control apparatus and method for an internal combustion engine, the engine having a variably operated engine valve in which at least a closure timing of an intake valve is variably controlled, which can achieve suppressions of a variation in an air-fuel ratio and a reduction in an engine driveability by preventing an unnecessary variation in fuel injection pulsewidth Tp in a case wherein the closure timing of the intake valve (IVC) is in the steady state while calculating the cylinder intake-air quantity so as to cope with a variation in the volume of the cylinder.
According to one aspect of the present invention, there is provided a fuel injection control apparatus for an engine having a variably operated engine valve in which at least a closure timing of an intake valve is variably controlled, the fuel injection control apparatus comprising: an intake valve closure state determining section that determines whether a closure timing of the intake valve is in a steady state or in a transient state; and a fuel injection quantity calculating section that calculates a volume of a cylinder from a control target value of the closure timing of the intake valve when the intake valve closure state determining section determines that the closure timing of the intake valve is in the steady state and from an actual closure timing of the intake valve when the intake valve closure state determining section determines that the closure timing of the intake valve is in the transient state, calculates a volume air quantity within the cylinder on the basis of the calculated volume of the cylinder and a fresh-air rate within the cylinder, calculates a mass air quantity sucked into the cylinder on the basis of a mass air quantity within an intake manifold of the engine calculated by income and outgo calculations of inflow and outflow quantities of a mass air within the intake manifold and a volume of the intake manifold, and calculates a fuel injection quantity on the basis of the mass air quantity sucked into the cylinder.
According to another aspect of the present invention, there is provided A fuel injection control method for an engine having a variably operated engine valve in which at least a closure timing of an intake valve is variably controlled, the fuel injection control method comprising: determining whether a closure timing of the intake valve is in a steady state or in a transient state; calculating a volume of a cylinder from a control target value of the closure timing of the intake valve when determining that the closure timing of the intake valve is in the steady state and from an actual closure timing of the intake valve when determining that the closure timing of the intake valve is in the transient state; calculating a volume air quantity within the cylinder on the basis of the calculated volume of the cylinder and a fresh-air rate within the cylinder; calculating a mass air quantity sucked into the cylinder on the basis of a mass air quantity within an intake manifold of the engine calculated by income and outgo calculations of inflow and outflow quantities of a mass air within the intake manifold and a volume of the intake manifold; and calculating a fuel injection quantity on the basis of the mass air quantity sucked into the cylinder.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.